JPH0412544B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a system in which frequency-modulated audio signals are alternately transmitted to a track inclined with respect to the running direction by two rotating magnetic heads, overlapping in some periods. The present invention relates to an audio signal reproducing device for reproducing audio signals from a magnetic tape recorded on a magnetic tape.

BACKGROUND TECHNOLOGY AND PROBLEMS For example, when recording video and audio signals on a magnetic tape, the normal recording method uses a frequency-modulated luminance signal on the high-frequency side and a carrier color signal that is frequency-converted on the low-frequency side. The mixed video signal is recorded alternately on a video track tilted with respect to the running direction of the tape by two rotating magnetic heads overlapping in some periods, and the audio signal is recorded on a fixed magnetic head without being modulated. The recording is performed on an audio track on one side of the tape that extends in the running direction of the tape.

In such a recording system, by slowing down the running speed of the magnetic tape and recording video signals at high density so that adjacent video tracks are adjacent to each other, long-time recording becomes possible. However, when recording video signals at high density by slowing down the running speed of the magnetic tape, the relative speed between the rotating head and the tape can be maintained at a speed sufficient to record video signals, but it is difficult to record audio signals. The relative speed between the fixed head and the tape is slowed, and the quality of the recorded audio signal is degraded.

Therefore, a method has been considered in which the quality of the audio signal is avoided by frequency modulating the audio signal, mixing it with the video signal, and recording the signal on a track inclined with respect to the running direction of the tape using a rotating head.

In this way, frequency-modulated audio signals are recorded alternately on a magnetic tape by two rotating heads on a track inclined with respect to the running direction.
To reproduce an audio signal, the track is alternately reproduced by two rotating heads, the frequency-modulated audio signal is separated and extracted from the reproduction output of each head, and the frequency-modulated audio signal is separately extracted. The frequency demodulation circuit demodulates the audio signals to obtain demodulated audio signals, and the two demodulated audio signals are alternately switched and extracted using a switch.

Since frequency-modulated audio signals are also recorded overlappingly during some periods, the frequency-modulated audio signals are recorded alternately and overlappingly during some periods in the playback output of the two rotary heads. The outputs of the two frequency demodulation circuits corresponding to the two rotating heads include the first
As shown in the upper part of the figure, two demodulated audio signals L _A and L _B are obtained alternately and overlappingly during some period T _x , and these signals L _A and L _B are converted into a switching signal SW. Therefore, the reproduced audio signal L is obtained by alternately taking out the signals using a switch that is switched at the center of the overlapping period T _x .

By the way, in this case, skew may occur or
There is a difference in the amount of protrusion of the two rotating heads from the drum surface, and the angular spacing between the two rotating heads is exactly 180°.
Otherwise, as shown in the lower part of FIG. 1, the phases of the two demodulated audio signals L _A and L _B output from the two frequency demodulation circuits will be shifted.
In this way, the two demodulated audio signals
If the phase of L _A and L _B is shifted, the waveform of the reproduced audio signal L obtained from the switch will become discontinuous at the joint between the signals L _A and L _B. If this reproduced audio signal L is output as is, generates noise at its discontinuous stores.

However, it is also possible to make the waveform of the reproduced audio signal L continuous by supplying the reproduced audio signal L obtained from the switch to a low-pass filter having a relatively low cutoff frequency. However, in this case, the high frequency components of the reproduced sound signal L are lost,
By frequency modulating the audio signal and recording it on a track inclined with respect to the running direction of the tape, the purpose of increasing the quality of the audio signal is lost.

Purpose of the Invention In view of the above, the present invention provides the following advantages by switching and extracting two demodulated audio signals output from two frequency demodulation circuits using a special switching circuit.
Even when the phases of two demodulated audio signals are shifted, a reproduced audio signal with a continuous waveform can be obtained, thereby improving the quality of the audio signal.

SUMMARY OF THE INVENTION In the present invention, the aforementioned switching circuit is configured to switch between the demodulated audio signal of the output of one of the two frequency demodulation circuits during the period in which the demodulated audio signal is obtained only at the output of one of the two frequency demodulation circuits. An audio signal is taken out as an output, but especially in a period when the demodulated audio signals are obtained redundantly at both outputs of the two frequency demodulation circuits, two demodulated audio signals of the outputs of the two frequency demodulation circuits are output. This overlap is caused by the state in which only the demodulated audio signal of the output of the frequency demodulation circuit whose output was the demodulated audio signal from before this overlapped period is added. until the state where only the demodulated audio signal of the output of the frequency demodulation circuit from which the demodulated audio signal is obtained is added to the output after the period obtained by
The configuration is such that the addition ratio is continuously changed and the added value is taken out as an output.

Embodiment FIG. 2 shows an example of a recording device corresponding to an example of the reproducing device of the present invention, in which a video signal and two channels of audio signals are recorded at high density on the same track inclined with respect to the running direction of the magnetic tape. This is the case.

That is, the two channels of audio signals L and R from the audio signal input terminals 11L and 11R are transmitted to the automatic gain control circuits 12L and 12R and the noise reduction circuit 13.
L and 13R, and pre-emphasis circuits 14L and 14R. and,
The audio signal L is supplied to frequency modulation circuits 15 and 16, and frequency-modulated audio signals LF _A and LF _B having carrier center frequencies of ₁ and ₂ are obtained. Also,
The audio signal R is supplied to frequency modulation circuits 17 and 18, and frequency-modulated audio signals RF _A and RF _B having carrier center frequencies of ₃ and ₄ are obtained.

Here, as shown in FIG. 4, the relatively narrow frequency band from the high frequency part of the low frequency-converted carrier color signal CL to the low frequency part of the frequency-modulated luminance signal YF, which will be described later, is the audio signal band. This band is divided into four bands of the same width, and the carrier center frequency is
₁ to ₄ are set as the center frequencies of each of the divided bands. However, as shown in the figure, ₁ < ₂ < f ₃
<f ₄ . Specifically, ₁ = _1.325MHz , ₂ =
_1.475MHz , ₃ = _1.625MHz , ₄ = _1.775MHz . Also, each signal LF _A , LF _B , RF _A , RF _B
The frequency deviation width is set to about 100 to 150 KH _Z.

Then, the frequency modulated audio signals LF _A and
RF _A passes through band pass filters 21 and 23 whose pass center frequencies are ₁ and ₃ to the mixing amplification circuit 25 _A.
and mixed and amplified. Further, the frequency-modulated audio signals LF _B and RF _B are supplied to the mixing amplification circuit 25B through the band pass filters 22 and 24 whose passing center frequencies are ₂ and ₄ , and are mixed and amplified.

On the other hand, a video signal from a video signal input terminal 1 is supplied to a low-pass filter 2 to extract a luminance signal Y, which is supplied to a frequency modulation circuit 3 to obtain a frequency-modulated luminance signal YF.
In addition, in the frequency modulated luminance signal YF,
For example, the leading edge of the synchronization signal is set to _4MHZ , and the white peak is set to _5.2MHZ . Also, the video signal from the video signal input terminal 1 is supplied to the bandpass filter 5, and the color subcarrier frequency is 3.58MHZ _.
The carrier color signal C is taken out and supplied to the frequency conversion circuit 6 to obtain a low frequency converted carrier color signal CL having a color subcarrier frequency _C of, for example, _688KHz . In addition, in this frequency circuit 6, the carrier color signal CL, which has been low-frequency converted, is used to remove crosstalk components from adjacent tracks during playback.
The phase of is controlled. Then, the frequency-modulated luminance signal YF and the low-pass converted carrier color signal CL
However, the high-pass filter 4 and the low-pass filter 7
The signals are supplied to the mixing amplification circuit 8 through the mixing amplification circuit 8, where they are mixed and amplified.

Note that, as shown in FIG. 4, the level of the carrier color signal CL is made smaller by the level of the luminance signal YF,
Frequency modulated audio signals LF _A , LF _B , RF _A ,
The level of RF _B and the level of the carrier color signal CL are further reduced, and the signals LF _A , LF _B , RF _A ,
During RF _B , the higher the carrier center frequency, the higher the level.

A mixed signal of the frequency-modulated luminance signal YF and the low-frequency-converted carrier color signal CL obtained from the mixing amplifier circuit 8 is a frequency-modulated audio signal LF _A ,
The signal is extracted through a band elimination filter 9 that removes signal components in the audio signal band so as not to interfere with LF _B , RF _A , and RF _B .

Then, the video signal obtained through the band elimination filter 9 and the frequency-modulated audio signals LF _A and RF _A obtained through the mixing amplifier circuit 25A are supplied to the mixing amplifier circuit 26A, where they are mixed and amplified, and the mixed signal is rotated. The tape is supplied to the head 27A, and recorded by the head 27A on every other track T _A that is inclined with respect to the running direction of the tape, as shown in FIG. In addition, the video signal obtained through the band elimination filter 9 and the mixing amplification circuit 25
Frequency modulated audio signal obtained through B
LF _B and RF _B are supplied to the mixing amplification circuit 26B, where they are mixed and amplified, and the mixed signal is sent to the rotary head 2.
7B and recorded on every other remaining track T _B by head 27B. The rotating heads 27A and 27B have an angular spacing of 180 DEG from each other, and tracks T _A and T _B are formed alternately for each field.

The heads 27A and 27B have different azimuth angles, and as shown in FIG. 3, the tracks T _A and T _B are formed in high density so that there is no gap between them.

FIG. 5 shows an example of the playback device of the present invention, which corresponds to the recording device shown in _FIG.
A mixed signal of the video signal and frequency-modulated audio signals LF _A and RF _A is reproduced by the rotary head 27A, and from the track T _B , the mixed signal is reproduced by the rotary head 27B.
The video signal and frequency modulated audio signal are
A mixed signal of LF _B and RF _B is reproduced.

Then, the reproduced output obtained from the track T _A by the head 27A is supplied to band pass filters 51 and 53 with pass center frequencies ₁ and ₃ through a regenerative amplifier circuit 28A, so that the carrier center frequency is _1.
and ₃ frequency modulated audio signals LF _A and RF _A
is taken out. Further, the reproduced output obtained from the track T _B by the head 27B is supplied to band pass filters 52 and 54 whose pass center frequencies are ₂ and ₄ through a regenerative amplifier circuit 28B, and frequency modulated whose carrier center frequencies are ₂ and ₄ . The resulting audio signals LF _B and RF _B are extracted.

Frequency modulated audio signals LF _A , obtained through filters 51 , 52 , 53 , 54 ,
LF _B , RF _A , RF _B are amplitude limiting circuits 55 , 56 ,
Frequency demodulation circuits 59, 60,
61 and 62, and from the frequency demodulation circuits 59 and 60, the demodulated audio signals L _A and L _B of one channel are overlapped for each field in a part of the period as shown in FIG. obtained alternately,
This is extracted through low-pass filters 63 and 64, and from frequency demodulation circuits 61 and 62, the demodulated audio signals R ₄ and R _B of the other channel are extracted.
are similarly obtained alternately for each field overlapping in some periods, and this is obtained by the low-pass filter 6.
5 and 66. Then, the demodulated audio signals L _A and
L _B , R _A and R _B are special switching circuits 70L, 70R
supplied to

On the other hand, based on a pulse signal indicating the rotational angular position of the rotating heads 27A and 27B, which is obtained from a pulse generator provided in connection with the rotation mechanism of the rotating heads 27A and 27B, a seventh As shown in the figure, two demodulated audio signals L _A and L _B , R _A and R _B are obtained overlapping periods T _AB , T _BA and audio signals L _A and L _B , R _A and R _B A signal SG whose level changes binary in periods T _A and T _B in which only one of them is obtained, and a signal SG whose level changes binary in periods T A and T B, and periods T _AB and T _BA
A signal that inverts every field at the center of
SW is obtained. Furthermore, these signals SG and SW
is supplied to the switching control voltage generating circuit 90, and the circuit 90 generates the audio signals L A , L _A , as shown in FIG.
In the period T _A when only R _A is obtained, the lowest value V _L is reached,
During the period T _B where only the audio signals L _B and R _B are obtained, the highest value V _H is reached, and the audio signals L _A and L _B , R _A and R _B overlap when transitioning from the period T _A to the period T _B. In _the period _{T AB obtained by}
Period during which L _A and L _B , R _A and R _B are obtained overlappingly
At T _BA , a switching control voltage V _X that changes linearly from V _H to V _L is obtained. This switching control voltage _VX is then supplied to switching circuits 70L and 70R.

In _the switching circuits 70L _{and 70R} , the switching _{control voltage V At T B , since the voltage V _} , R _A and R _{B overlap} , corresponding to the voltage V _X changing directly from V _L to V _H , the audio signals L _A and L _B ,
The output is the sum of R _A and R _B with the addition ratio continuously changed from a state where only signals L _A and R _A are added to a state where only signals L _B and R _B are added. During the period T _BA where the audio signals L _A and L _B , R _A and R _B are obtained overlappingly when transitioning from the period T _B to the period T _A , the voltage V _X increases from V _H to V _L. In direct response to changes in the audio signal
L _A and L _B , R _A and R _B are in a state where the addition ratio is continuously changed from a state where only signals L _B and R _B are added to a state where only signals L _A and R _A are added. The sum is taken out as the output.

In short, the switching circuits 70L and 70R are adder circuits whose addition ratios can be changed, and the output reproduced audio signals L and R change the addition ratio of the audio signals L _A and R _A to x,
Assuming that the addition ratio of audio signals L _B and R _B is 1-x, L=xL _A + (1-x) L _B , R=xR _A + (1-x)
In period T _{A ,} x=1 and L=L _A ,
R = R _A , and in period T _B , x = 0, L = L _B ,
R= _RB , and in the period T _AB , x changes continuously from 1 to 0, and in the period T _BA , x changes continuously from 0 to 1.

Therefore, when the two demodulated audio signals L _A and L B and R _A and R _B are out of phase, the reproduced audio signals L and _R output from the switching circuits 70L and 70R are as shown in FIG. These two demodulated audio signals L _A
and the period T _AB where L _B , R _A and R _B are obtained overlappingly,
In T _BA , as shown by the broken line in the figure, even if the phases of the two demodulated audio signals L _A and L _B and R _A and R _B are shifted, their waveforms remain continuous. The reproduced audio signals L and R, which have continuous waveforms obtained from the switching circuits 70L and 70R, respectively, are sent to the audio signal output terminals 69L and 6 through the day emphasis circuits 67L and 67R, and further through the noise reduction circuits 68L and 68R.
It is derived from 9R.

On the other hand, the rotary head 27 is connected to the tracks T _A and T _B.
The reproduced outputs obtained by A and 27B are supplied to the input terminals A and B of the switch 29 through the regenerative amplifier circuits 28A and 28B, and the switch 29 is activated during the period T _BA by the signal SW obtained from the signal generating circuit 80 described above. In the period from the middle point in time to the middle point in period T _AB , the input terminal is switched to the A side, and in the period from the middle point in period T _AB to the middle point in period T _BA , it is switched to the input terminal B side. , a continuous reproduction output is obtained from the switch 29. Then, this continuous playback output is passed through the band removal filter 3.
0, the frequency-modulated audio signals LF _A , LF _B , RF _A , RF _B are removed from the playback output, and this audio signal is low-frequency converted with the removed frequency-modulated luminance signal YF. The video signal mixed with the carrier color signal CL is supplied to a video signal reproduction system.

In the video signal reproduction system, a video signal obtained through a band elimination filter 30 is supplied to a high-pass filter 31, which converts the frequency-modulated luminance signal into a high-pass filter 31.
YF is extracted and supplied to the frequency demodulation circuit 33 through the amplitude limiting circuit 32 to obtain a demodulated luminance signal Y. This luminance signal Y is led out to the luminance signal output terminal 35 through the low-pass filter 34. Ru. Further, the video signal obtained through the band removal filter 36 is supplied to the low-pass filter 36, and a low-pass converted carrier color signal CL is taken out. This is supplied to the frequency conversion circuit 37, and the color subcarrier frequency is A carrier color signal C returned to 3.58MH _Z is obtained. Note that in this frequency conversion circuit 37, the phase of the carrier color signal C is restored to its original state. This carrier color signal C is then supplied to a comb-shaped characteristic filter 39 through a bandpass filter 38 to remove crosstalk components from adjacent tracks. It is led out to the output terminal 40.

Figure 6 shows a specific example of the switching circuits 70L and 70R.
The collector of a transistor 73 is connected to the emitters of transistors 71 and 72 to form a differential amplifier circuit 7.
4 is configured, the collector of a transistor 77 is connected to the emitters of transistors 75 and 76 to configure a differential amplifier circuit 78, and a constant current source 79 is connected to the emitters of transistors 73 and 77. 72 and 76
A load resistor R _L common to the amplifier circuits 74 and 78 is connected to the collector of the transistor 71, demodulated audio signals L _A and R _A are supplied to the base of the transistor 71, and the demodulated audio signal L _B is supplied to the base of the transistor 75. ，
R _B is supplied to the base _of the transistor ₇₇ , the switching control _{voltage V} A constant voltage V _O with an intermediate value is applied, and the reproduced audio signals L and R are output from the collectors of the transistors 72 and 76.
is taken out.

The gain of the amplifier circuits 74 and 78 is determined by the transistor 7.
Determined by the currents _A and _B flowing through 3 and 77, the current
_A and _B vary differentially depending on the switching control voltage _VX . _That is _{, when the voltage V} All of the currents 79 flow through the transistor 77, so that _A =0, _B =, and when the voltage _VX is _V0 , _A = _B =1/2. Therefore, assuming that x changes between O and 1, the gains of the amplifier circuits 74 and 78 are relatively x,
The output signals L and R obtained at the collectors of transistors 72 and 76 are expressed as L=xL _A +(1-X)L _B , R=xR _A +(1-x )
Represented by R _B. As shown in FIG. 7, during the period T _A in which only the audio signals L _A and R _A are obtained, _A
=, _B = 0, x = 1, and the audio signal L _B ,
In period T _B where only R _B is obtained, _A = O, _B =
Then, x = 0, and in the period T _AB where the audio signals L _A and L _B , R _A and R _B are obtained overlappingly when transitioning from the period T _A to the period T _B , _A is linear from to 0. conversely, _B directly increases from 0, x decreases linearly from 1 to 0, and the audio signals L _A and L _B when transitioning from period T _B to period T _A , In the period T _BA where R _A and R _B overlap, _A increases linearly from 0 to 0, _B decreases linearly from 0 to 0, and x increases linearly from 0 to 1. do.

Effects of the Invention According to the present invention, a magnetic tape in which frequency-modulated audio signals are alternately recorded on a track inclined with respect to the running direction by two rotary recording heads, overlapping in some periods. When reproducing audio signals, the frequency-modulated audio signals obtained from the two reproducing rotary heads are demodulated separately.
A switching circuit that switches and extracts the two demodulated audio signals from the outputs of the two frequency demodulation circuits and cuts off the consecutively reproduced audio signals is connected to the output of only one of the two frequency demodulation circuits. During the period when an audio signal is obtained, the demodulated audio signal of the output of one of the frequency demodulation circuits is taken out as an output, but in particular, the demodulated audio signals of the output of both frequency demodulation circuits overlap. In the period obtained by the overlapping period, the two demodulated audio signals output from these two frequency demodulation circuits are at the frequency of the one from which the demodulated audio signal was obtained before the overlapped period. From the state where only the demodulated audio signals of the output of the demodulation circuit are added, the demodulated audio signal of the output of the frequency demodulation circuit is obtained at the output after this overlapping period. Since the configuration is such that the addition ratio is continuously changed until only the audio signals are added, and the sum is taken out as the output, the two outputs of the two frequency demodulation circuits may be Even if the phase of the demodulated audio signal is shifted, a reproduced audio signal with a continuous waveform can be obtained, and the quality of the audio signal can be improved.

[Brief explanation of drawings]

Fig. 1 is a waveform diagram for explaining the purpose of the present invention, Fig. 2 is a connection diagram showing an example of a recording device corresponding to an example of the reproducing device of the invention, and Fig. 3 is a tape diagram for explaining the same. FIG. 4 is a diagram showing an example of the frequency spectrum of a recorded signal for explanation thereof. FIG. 5 is a connection diagram showing an example of the reproducing apparatus of the present invention. FIG. A connection diagram showing a specific example of the main switching circuit, and FIG. 7 is a waveform diagram for explaining its operation. In the figure, 27A and 27B are rotating magnetic heads;
1-54 are band pass filters, 55-58 are amplitude limiting circuits, 59-62 are frequency demodulation circuits, 63-
66 is a low-pass filter, 70L and 70R are switching circuits, and 90 is a switching control voltage generation circuit.

Claims (1)

[Claims] 1 Frequency-modulated audio signals are recorded alternately by two rotating magnetic heads for recording on a track inclined with respect to the running direction, overlapping in some periods, from a magnetic tape. Playing audio signals alternately and overlappingly in some periods 2
a rotating magnetic head for reproduction, two frequency demodulation circuits that separately demodulate the frequency-modulated audio signals obtained from the two rotating magnetic heads for reproduction, and outputs of the two frequency demodulation circuits. and a switching circuit that switches and extracts the two demodulated audio signals to obtain a continuous reproduced audio signal, and this switching circuit selects the demodulated audio signal to output only one of the two frequency demodulation circuits. During the period when a signal is obtained, the demodulated audio signal of the output of one of the frequency demodulation circuits is taken out as an output, and the demodulated audio signals of the outputs of both of the above two frequency demodulation circuits are obtained in duplicate. In the period of
The two demodulated audio signals from the outputs of these two frequency demodulation circuits are demodulated from the output of the frequency demodulation circuit from which the demodulated audio signal had been obtained before the overlapped period. From the state in which only the audio signals that are output are added, only the demodulated audio signals of the output of the frequency demodulation circuit whose output is the demodulated audio signal that is obtained after this overlapped period are added. An audio signal reproducing device in which the addition ratio is continuously changed until the addition ratio is changed until the output is output.